From: | Greg Smith <greg(at)2ndquadrant(dot)com> |
---|---|
To: | Scott Carey <scott(at)richrelevance(dot)com> |
Cc: | Ireneusz Pluta <ipluta(at)wp(dot)pl>, "pgsql-performance(at)postgresql(dot)org" <pgsql-performance(at)postgresql(dot)org> |
Subject: | Re: 3ware vs. MegaRAID |
Date: | 2010-04-08 06:13:32 |
Message-ID: | 4BBD740C.7020308@2ndquadrant.com |
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Lists: | pgsql-performance |
Scott Carey wrote:
> * Change the linux 'readahead' block device parameter to at least 4MB (8192, see blockdev --setra) -- I don't know if there is a FreeBSD equivalent.
>
I haven't tested them, but 3ware gives suggestions at
http://www.3ware.com/kb/Article.aspx?id=14852 for tuning their cards
properly under FreeBSD. You cannot get good sequential read performance
from 3ware's cards without doing something about this at the OS level;
the read-ahead on the card itself is minimal and certainly a bottleneck.
As for your comments about drives being faster at the front than the
end, the zcav tool that comes with bonnie++ is a good way to plot that
out, rather than having to split partitions up and do a bunch of manual
testing.
--
Greg Smith 2ndQuadrant US Baltimore, MD
PostgreSQL Training, Services and Support
greg(at)2ndQuadrant(dot)com www.2ndQuadrant.us
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